Personally, after doing some research, there isn't really any difference...
One has an amp, and one doesn't.
It has nothing really to do with how tight the bass sounds.
The only difference that may be, is if the sub has an amp in it, like an Active does, then the equalisation may be slightly better, since it isn't controlled by passive crossovers, so it can be programmed more for the sub in question.
In terms of performance though, there isn't really much in it I don't think.
BUT, In terms of features,
I'd prefer a passive, as the amp you'd have to use with it is probably a lot better to manually configure, and may offer more sound features.